Heretofore, there is known an apparatus arranged to irradiate illumination light from an illumination light source toward a cornea and receive reflection light from the cornea through an imaging element (an image pickup element) to obtain an image of corneal endothelial cells in non-contact relation.
As an apparatus of this type, for example, there are known an apparatus provided with a focus detecting sensor for detecting a focus state with respect to corneal endothelium and arranged to move an apparatus main unit to a focus position of the endothelium and then take photographs (see JP 8(1996)-206080A) and an apparatus arranged to consecutively take photographs while moving an apparatus main unit in a predetermined direction (JP 7(1995)-79924A).
Meanwhile, the endothelial cells have to be observed at high powers (magnifications). Thus, high alignment accuracy is demanded. As an alignment detecting sensor for detecting alignment marks or indexes projected on a cornea, for example, a position sensor (PSD) is conventionally used. The positional information in an X direction and the positional information in a Y direction output from the position sensor are detected respectively to perform alignment (see FIGS. 10A and 10B).